Preparation of food often involves cooking. Grills, usually of the type used outdoors, are used to prepare meat, fish and vegetables and are considered by many to lend a unique flavor to such foods and to the ambience surrounding their preparation. Heat sources commonly used in such grills include gas and charcoal. The popularity of outdoor cooking grills is evident from the fact that there are well over 2.5 million outdoor grills sold in the United States each year.
Earlier cooking grills include a kettle within which is placed an intermediate "barrier" embodied as a rack interposed between the burner and the food-supporting grate. The rack supports individually-placed ceramic briquettes or lava rocks arranged in a way to help distribute heat toward the outer edges of the grill. And most of the grease and other liquid dripping from the food lands on the briquettes or rock rather than on the burner. Flame "flare-ups" are thereby substantially avoided.
A disadvantage of rack-supported briquettes or lava rocks is that they must be rather precisely placed with consistent rock-to-rock spacing to avoid "hot spots." And if a user moves the cooking grill to a new location, there is a high likelihood that even with precise initial placement, the positions of some rocks will change and will not be re-adjusted.
More recently, manufacturers of such cooking grills have used a metal heat distribution plate as the intermediate barrier in place of the rack and briquette or rock. Plates of this type (which are sized and shaped to fit a particular cooker kettle) have holes, e.g., slits or the like, placed in selected locations. Such locations are selected to distribute heat toward the edges of the cooking grate. And the mere presence of the plate helps stop grease and other liquids from dripping onto the burner or to the bottom of the kettle.
Since such plates rust and/or otherwise deteriorate over time, there is a growing market for replacement heat distribution plates. Rock-supporting racks are also subject to deterioration and owners of grills having such racks are increasingly using heat distribution plates as a replacement substitute therefor. While replacement heat distribution plates are available from the grill manufacturer (and perhaps from others), each is a one-piece plate sized and shaped to fit a particular kettle. Kettles ranging in size from 8" wide by 13" long to 14.5" wide by 24.5" long are commonly used as components of cooking grills.
Examples of cooking grills and similar products are shown in U.S. Pat. Nos. 3,288,050 (Saiki); 4,703,746 (Hitch) and 5,101,805 (Noh). The Saiki patent shows a circular, disc-like adjustable food-supporting grate particularly suited for an hibachi. The grate has two stacked plates concentric with one another and relatively adjustable one to the other in use. The plates are custom sized to fit the open-topped "mouth" of the hibachi or fire pot with which they are used and cannot be adapted to fit a variety of hibachi or pot sizes.
The Hitch and Noh patents both show heat control mechanisms using two grate-like members one above the other. Such mechanisms are configured to fit a kettle (Hitch) or an oven (Noh) of a particular size. For either type of heat control mechanism, all of the openings across the entire cooking surface area are required to be open or partially or fully occluded to the same degree. That is, there is no way for openings near the center of the members to be more fully closed than those near the edges of the members.
A commonly-available heat distribution plate is shown in a Thermos.RTM. product catalog sheet. Such plate is said to fit all Structo.RTM. and Thermos.RTM. 42,000 BTU grills; that is, the plate is dimensioned (in length and width) for a particular kettle size. Commonly-available kettle sizes are as follows: 11.5 inches by 19 inches; 12.75 inches by 19 inches; 14.5 inches by 21.5 inches; 15.5 by 24.5 inches and 15 inches by 26.5 inches. However, there are a few variations from these more-or-less standard sizes and other variations may be developed in the future.
While these prior art products involving heat distribution plates and lava rock arrangements have been generally satisfactory, they are nevertheless attended by certain disadvantages. One disadvantage (which is very pronounced in grills with lava rock arrangements) is that the temperature "gradient" of the cooking grate, i.e., the difference in grate temperature between the hottest area and the coolest area, can be very substantial.
The magnitude of the temperature gradient and the precise locations of those parts of the grate cooking surface which are hottest and coolest tend to vary with specific grill configuration, with the direction of any wind-related draft and according to whether the grill is equipped with a heat distribution plate, with a rack holding lava rocks or with neither. However, a few general observations can be made.
With neither a heat distribution plate nor a rock rack, the hottest part of the grate is usually at the center directly above the burner. With either a heat distribution plate or a rock rack, the usual hottest area of the cooking surface is at the rear of the grate where heat is "ventilated." The coolest areas of such surface are at the grate corners. And generally, the front portion of the cooking surface toward the user is somewhat cooler than the rear portion.
The following helps appreciate the effect of temperature gradient upon the quality of the cooked food product. When a cooking grill exhibits a temperature gradient of less than about 140.degree.-160.degree. F. (which is relatively common when the grill has a custom-sized heat distribution plate and rare with grills using lava rock), food need not be periodically moved on the grate to obtain relatively uniformly cooked product.
But as the magnitude of the gradient increases above about 140.degree.-160.degree. F., the more imperative it becomes to move food, e.g., hamburgers, from place to place on the cooking surface to obtain a uniformly-cooked product. Users of grills, especially of the type having lava rock or briquettes as a means of heat distribution, are all-too-familiar with burgers which are well done at those portions nearer the rear of the grate and rare or even raw at those portions nearer the grate front or corners.
As an example of the magnitude of commonly-occurring temperature gradients, tests were conducted on a kettle measuring 15 inches between the front and rear sides and 26.5 inches between the lateral kettle ends. Such kettle was equipped with a conventional heat distribution plate (as may be furnished by the grill original equipment manufacturer or "OEM") and the temperature gradient across the cooking grate was about 130.degree. F. The hottest temperature, about 775.degree. F., was at the grate rear portion and the coolest temperature, about 645.degree. F., was at the grate corners. Similarly-measured temperature gradients involving smaller kettle sizes were less than 130.degree. F.
As another example, tests on the same kettle equipped with a rack supporting lava rock (as may also be furnished by the grill OEM) demonstrated that the temperature gradient was about 285.degree. F. The hottest temperature, about 980.degree. F., was at the grate rear portion and the coolest temperature, about 695.degree. F., was at and near the grate corners. Such gradients in smaller kettle sizes ranged above and below 285.degree. F.
A characteristic of prior art arrangements is that lava rock support racks and heat distribution plates are dimensioned to fit a particular kettle size. Several disadvantages result. Since there are at least five sizes of rectangular kettles used with currently-available cooking grills, the rack or plate manufacturer (especially one selling such racks or plates in the replacement market) must make and stock all sizes or forego sales as to those sizes not produced.
Similarly, distributors and other re-sellers of such products must carry a rather substantial inventory of racks and/or plates to broadly meet the needs of their customers. Inventory, especially a large inventory, has unfavorable implications involving inventory carrying costs and warehouse space.
Another disadvantage is that because of the "size-specificity" of the racks and plates, they do not lend themselves to sale in kit form for universal application in grill kettles of any of a variety of sizes. It might be said that they lack "universality" in application.